Marine Benthic Algae of the Houtman Abrolhos Islands, Western Australia. John M. Huisman School of Biological and Environmental Sciences, Murdoch University Murdoch, Western Australia 6150, Australia Abstract Recent collections and published records of marine benthic algae from the Houtman Abrolhos are catalogued. Two hundred and sixty species are included, comprising 32 species of green algae (Chlorophyta), 50 species of brown algae (Phaeophyta), and 178 species of red algae (Rhodophyta). Fifty-three species and four varieties are newly recorded for the Indian Ocean coast of Western Australia. The algal flora of the islands includes a mixture of typically temperate species (e.g. the kelp Ecklonia radiata (C. Agardh) J. Agardh) along with many species usually found at more northern latitudes in tropical waters (e.g. the red alga Trichogloea requienii (Montagne) Kiitzing). Introduction The Houtman Abrolhos is a group of mainly coral islands lying some 50-70 km offshore from Geraldton, Western Australia. They include the most southerly coral reefs in the Indian Ocean, and no doubt owe their presence to the influence of the Leeuwin Current, which brings warm waters from the tropics along the coast of Western Australia. The influence of the Leeuwin Current can be sporadic, and this juxtaposition of warm tropical water with the colder water more typical of these latitudes encourages unusual associations and contributes to a wide diversity of organisms (Hatcher 1991). The marine algae of the islands are poorly known, with only sporadic records appearing in the literature (e.g. Levring 1953; May 1946, 1951; Lucas 1926), mostly derived from collections made by the 'Percy Sladen Trust' expeditions of 1913 and 1915 (see Dakin 1918-1922) or collections made by school groups and presently lodged in the Adelaide herbarium. These publications include, at most, only a few species. During the past ten years the author has made regular trips to the islands to collect marine algae, resulting in the descriptions of several new taxa (e.g. Kraft & Wynne 1992; Huisman & Kraft 1992, 1994; Huisman 1994; Huisman & Gordon-Mills 1994; Huisman & Millar 1996) and a collection of well over a thousand specimens. The present account includes all of the species recognised in those collections as well as all known published records. The account of the genus Sargassum was contributed by Gary Kendrick (CSIRO Marine Laboratories, Marmion, Western Australia). 178 J.M. HUISMAN Materials and methods All recent collections were preserved in 5% formaldehyde before being dried and mounted. Most specimens are housed in the herbarium of the School of Biological and Environmental Sciences, Murdoch University (MURU), except where otherwise indicated. Herbarium abbreviations follow Holmgren et al. (1990). Arrangement of the Cat\].logue All known species of marine benthic algae recorded from the Houtman Abrolhos are included. The majority are derived from recent collections made by the author and his associates, while a few taxa are known only through previously published accounts. The sequence of presentation is: Division Chlorophyta, Division Phaeophyta, Division Rhodophyta, with the lower level taxa (Order, Family, Genus, Species) within each division arranged in alphabetical order. The presently accepted binomial is given for each species, followed by the basionym, a recent reference, the type locality, distribution data, and selected specimens. Discussion The present account records some 260 species of marine benthic algae for the Houtman Abrolhos, comprising 32 species of green algae (Chlorophyta), 50 species of brown algae (Phaeophyta) and 178 species of red algae (Rhodophyta). Included are 53 species and four varieties newly recorded for the Indian Ocean coast of Western Australia (Table 1). This listing should not be regarded as comprehensive for the region, however, as there remain many specimens in the author's collection that could not be identified with any confidence due to inadequate material. The actual total number of species is likely to be well over 300. The marine flora of the islands is a diverse assemblage, and includes a mixture of species from both tropical and temperate origins. The former category includes typically tropical taxa such as Boodlea composita, Caulerpa webbiana, C. cupressoides, C. lentillifera, Trichogloea requienii, Acanthophora spicifera, Spirocladia barodensis, Predaea weldii, Titanophora weberae, and Ceratodictyon spongiosum. Examples of taxa with more temperate affinities are Caulerpa obscura, C. simpliciuscula, Codium laminarioides, Myriodesma quercifolium, Ecklonia radiata, Carpothamnion gunnianum, Hennedya crispa, and Erythroclonium sonderi. Many of these species are at the southernmost limit (in the case of tropical species) or northernmost limit (in the case of temperate species) of their distribution at the Houtman Abrolhos. The affinities of the marine algae of the Houtman Abrolhos are therefore suggestive of a transitional zone between tropical and temperate regions. That this should exist at a more southern latitude than would normally be expected is, no doubt, due to the influence of the Leeuwin current, which carries warm, tropical waters in a southerly direction along the coast of Western Australia (Cresswell 1991). This influx of warm water is also sporadic, a situation that is likely to further contribute to the diversity of algae found at the Houtman Abrolhos. Hatcher (1991) recognised the influence of the Leeuwin current on the marine algal assemblages on a broad scale - this is now confirmed by the more detailed listing included herein. Further collections and taxonomic studies of the many inadequately represented species are required before our knowledge of the marine algae of the Houtman Abrolhos can be regarded as comprehensive. The present account, however, is a significant addition to the recognition BENTHIC ALGAE OF THE HOUTMAN ABROLHOS 179 of the marine flora of the Houtman Abrolhos (and Western Australia), and is a first step in the description of the marine flora of the poorly known northern regions of Western Australia. Acknowledgements This study would not have been possible without the contributions of many individuals who have organised or participated in field trips. In particular I would like to thank Ian McKernan (Murdoch University) for his tireless efforts. I would also like to acknowledge the Western Australian Fisheries Department (in particular Randall Owen) for allowing the use of the field station at Beacon Island. Numerous people have acted as diving buddies and they are gratefully acknowledged, in particular Dr Thomas Rose (Murdoch University), Dr Gary Kendrick (CSIRO Marine Laboratories, Marmion), and Tim Carruthers (University of Western Australia). Drs Gerry Kraft (University of Melbourne), Gary Kendrick, Julie Phillips (University of Queensland), Ian Price (James Cook University, Townsville), Alan Millar (National Herbarium of New South Wales), Roberta Townsend (Murdoch University) and Professors Bryan Womersley (State Herbarium of South Australia) and Michael Wynne (University of Michigan) have all contributed to this study by identifying specimens or giving advice. Thanks also to Associate Professor M.A. Borowitzka (Murdoch University) for his support. Financial support was provided by an ARC 'Australian Research Fellowship' and an ARC small grant for the study of the marine flora of the islands. Table 1. Taxa newly recorded for Western Australia(* =new record for Australia). Rhodophyta Platysiphonia corymbosa Platysiphonia marginalis Amphiroa foliacea Polysiphonia gracilis Antithamnion antillanum Predaea laciniosa Botryocladia skottsbergii Predaea weldii Callophycus serratus Rhodymenia leptophylla Ceramium mazatlanense Spirocladia barodensis Champia parvula Titanophora weberae Chondria dangeardii Trichogloea requienii Chrysymenia kaernbachii Yamadaella caenomyce Chrysymenia ornata Chlorophyta Coelothrix irregularis Anadyomene brownii Corallophila huysmansii Boodlea composita Dasya iyengarii Dasya pilosa Bryopsis minor Endosiphonia spinuligera Caulerpa fergusoniii Caulerpa mexicana Gelidiella pannosa Caulerpa racemosa var. corynephora Gelidiopsis variabilis Caulerpa racemosa var. lamourouxii Glaphrymenia pustulosa Caulerpa racemosa var. peltata Gloiocladia indica * Caulerpa racemosa var. turbinata Gloiocladia rubrispora Caulerpa serrulata Gracilaria canaliculata Caulerpa webbiana Hypoglossum caloglossoides Codium geppiorum Kallymenia cribrogloea Dictyosphaeria versluysii Liagora setchellii * Trichosolen hainanensis Lomentaria corallicola Lomentaria monochlamydea Phaeophyta Qre Mesophyllum erubescens * Dictyota ceylanica * Jed Mesophyllum junafutiense * Dictyota mertensii * Monosporus indicus Padina boergesenii H on Peyssonnelia inamoena Padina tenuis 180 J.M. HUISMAN Division Chlorophyta Order Bryopsidales Family Bryopsidaceae Genus: Bryopsis Lamouroux 1809b: 333. Bryopsis australis Sonder 1845: 49. Reference: Womersley 1984: 284, figs 96D,E, 97B. Type Locality: Western Australia, probably near Fremantle. Distribution: Houtman Abrolhos, Rottnest Island and adjacent mainland coasts, Western Australia, and Kingscote and Ballast Head, Kangaroo Island, South Australia. Specimen: Nth of Beacon 1., Wallabi Gp. From 2-3 m. (J.M. Huisman, 8.vii.1993; MURU, HA 928). Bryopsis minor Womersley 1955: 387, fig. 1. References: Womersley 1955: 387; Womersley 1984: 276, figs 93A,B, 94A,B. Type Locality: On black buoy, American River inlet, Kangaroo Island, South Australia. Distribution: Houtman